1. Field of the Invention
The invention relates to a charging system and method for charging a communication terminal, such as a mobile communication terminal.
2. Background of the Related Art
In general, a battery for a mobile communication terminal includes three or four terminals that connect to a charger. If the battery includes three terminals, they are generally a (+) terminal, a (−) terminal, and an ID terminal. If the battery includes four terminals, a temperature checking terminal for checking temperature change of the battery is also included.
The ID terminal checks a capacity of the charged battery. The battery capacity can be determined from a resistance connected to the ID terminal. The value of the resistance is generally determined by the manufacturer. Because a resistance is generally provided between the ID terminal and the (−) terminal of the battery, a charger can determine a battery capacity by checking the resistance between the two terminals.
The charger is used to charge a battery attached to a mobile communication terminal. For example, a home charger or a travel charger receives AC power and converts it to DC power to generate a constant voltage, for example, 4.2V. On the other hand, a car-use charger or hands-free kit (HFK) reduces DC power, for example, 12V, a voltage for cars, to generate a constant voltage, for example, 4.2V, to perform the charging operation.
For the charger, a constant voltage/constant current circuit is used to provide a DC current for charging. If the battery receives only a low voltage for charging, charging is performed with the constant current. If the battery voltage goes up, charging is performed with the constant voltage. As charging is continuously performed, the charging current is gradually reduced.
A resistor provides resistance between the ID terminal and the (−) terminal of the battery, and is connected in series therewith, such that the current flows through the resistor. The charger measures the voltages at both ends of the resistor. If they are higher than a predetermined level, the charger determines that the battery has not been fully charged. However, if they are the same as, or lower than, the predetermined level, the charger determines that the battery has been fully charged.
FIG. 1 is a flow chart of a conventional art battery charging method for a mobile communication terminal.
As shown in FIG. 1, the conventional art battery charging method includes: checking an ID resistance value of a battery by verifying the battery capacity, step S110, applying a charging current corresponding to the battery capacity, step S120, checking a charging voltage or charging current input to the battery, step S130, determining whether battery charging has been completed, step S140, and displaying that battery charging has been completed on a display unit and turning off an output current of the charger, if the battery charging has been completed, step S150.
The operation of the conventional art battery charging method for a mobile communication will now be described in more detail.
In order to charge a battery attached to a mobile communication terminal, the battery is mounted in a charge slot provided in the charger. Then, the charger checks the ID terminal of the battery to determine the battery capacity, step S110. That is, the charger determines the battery capacity from a resistance value of the ID terminal of the battery. For example, if an ID resistance value of a battery having a capacity of 500 mAh is 2.4 KW and an ID resistance value of a battery having a capacity of 750 mAh is 4.7 KW, the charger can determine a capacity of the battery to be charged from the resistance value of the ID terminal.
After the charger determines the battery capacity, it applies a charge current corresponding to the battery capacity to the charge terminal of the battery, step S120. For example, if the battery capacity is 500 mAh, the charger applies a 500 mAh charge current, or if the battery capacity is 750 mAh, the charger applies a 750 mAh charge current.
After the charge current is applied, a charge voltage of the battery or an output current value of the charger is measured, step S130. If the measured battery charge voltage exceeds a predetermined voltage, a value of the current output from the charger is gradually reduced. For example, if the charger initially outputs a current of 500 mAh and if the battery charge voltage exceeds the predetermined voltage, the charger outputs a current value smaller than 500 mAh and then the value is reduced gradually.
Accordingly, if the battery charge voltage is greater than the pre-set reference voltage or if the charge current output from the charger is smaller than the pre-set reference current, it is determined that the battery charging has been completed, step S140. Then, a charging completion message is displayed on a display unit, and the current output from the charger is turned off, step S150.
While the battery of the mobile communication terminal is being charged, a message is displayed indicating that the battery is being charged and the mobile communication terminal may perform certain operations at the same time, providing convenience for a user. For example, in order to display the fact that the battery is being charged at the mobile communication terminal, a liquid crystal screen backlight and a keypad backlight of the terminal are operated. In other words, a battery bar displayed on the liquid crystal screen is scrolled or characters such as ‘battery charging’ are output, so that the user is aware of the processes being performed by viewing the liquid crystal screen of the mobile communication terminal. In addition, the user can instruct the mobile communication terminal to perform certain operations during the battery charging, such as searching a previously stored number by depressing a key button on the mobile communication terminal, or performing a menu manipulation in order to change a setting of the mobile communication terminal.
However, during operation of the backlight of the liquid screen display and keypad and during mobile communication terminal manipulation by the user, the mobile communication terminal consumes a current supplied from the charger. That is, the charger performs the battery charging by outputting only a pre-set current value corresponding to the battery capacity, which does not take into account the amount of current consumed by the mobile communication terminal. Therefore, if the current consumption of the mobile communication terminal increases, the amount of current charged to the battery is reduced, resulting in a problem that the time taken to complete the battery charging increases.